Video monitors which display images generated by a computer are manufactured in a variety of types and in a variety of sizes. Different monitors require different control signals from the computer. Some monitors require control signals from the computer that establish a single specific degree of resolution in the image and the required resolution is different in different types of monitor. Most newer monitors are designed to enable operator selection of any of several specific resolutions. Thus the computer must provide different control signals to different monitors or to a single monitor if the operator wishes to change resolution.
Newer computers of the well known type manufactured by Apple Computer, Inc. and which are generally referred to by the trademarked name "Macintosh" or "Mac" are available with an internal monitor controller built into the motherboard and which is known as "On Board Video". The controller is designed to sense the type of monitor to which it is connected provided that the monitor contains components which generate a resolution code that identifies the required resolution. The computer then provides monitor control signals that establish that particular resolution.
The original resolution coding, termed the "Sense Line Protocol" by Apple Computer, Inc., provided for seven different resolution codes. The system has since been extended and expanded to provide for additional codes.
Monitors designed for use with other types of computer, such as the MS-DOS type manufactured by IBM Corporation for example, do not have the resolution code generating components and also have cable connectors that differ from those of the Macintosh computers. Many of these monitors have capabilities that can be highly useful to users of Macintosh computers.
Adaptors have recently been introduced to the market which are designed to enable interfacing of the otherwise incompatible monitors and Macintosh computers. Adaptors of this kind have a pin conector at one end that engages in the video port of the computer and a differing connector at the other end that conforms with the connector at the end of the monitor image data input cable. These recently commercialized adaptors also contain components for producing the resolution code that the computer needs to sense in order to provide a resolution that is appropriate to the particular monitor but are subject to a number of limitations in this respect.
Some adaptors of this kind are hardwired and thus can produce only a single code. This requires that a series of differing adaptors be manufactured in order to meet the needs of different monitors and/or to provide different resolutions. Other adaptors of this kind enable selection of any of a series of codes but have switching arrangements, such as plural dip switches that are difficult to adjust and which can be confusing to the user.
The adaptors do not address other problems that can be encountered in interfacing monitors and computers including monitors and computers of the same manufacture. For example, such adaptors do not enable adjustments to accommodate to the different synchronization signal input requirements of different types of display monitor.
The present invention is directed to overcoming one or more of the problems discussed above.